1. Field of the Invention
The present invention relates to an ignition apparatus for internal combustion engine. More specifically, this invention relates to the ignition apparatus that has a function to generate a firing voltage (Hereinafter referred to as xe2x80x9ca high voltage for firingxe2x80x9d) in the ignition coil for generating the spark discharge between electrodes of a spark plug and to supply an ionized current after a spark discharge.
2. Description of the Related Art
In internal combustion engines used in such as vehicle engines, when an air-fuel mixture is ignited by a spark discharge that is generated by a spark plug, ion is generated following this firing. Therefore, after the air-fuel mixture is ignited by the spark discharge of the spark plug, an ionized current flows by supplying a voltage between electrodes of the spark plug. As the amount of the generated ion changes with ignited conditions of the air-fuel mixture, the ionized current generating by the generated ion is detected and analyzed, whereby to carry out a misfire detection or knocking detection.
In the conventional ignition apparatus for internal combustion engine, which has a function for generating the ionized current, the spark plug is electrically connected to one end of a secondary winding while a capacitor is provided in series to the other end thereof;
when the spark discharge generates at the spark plug, the capacitor is charged by a spark discharge current (Hereinafter, referred to as xe2x80x9csecondary currentxe2x80x9d) flowing in the secondary winding of the ignition coil and the spark plug;
the charged capacitor is discharged after stopping the spark discharge, whereby a voltage is supplied between electrodes of the spark plug through the secondary winding (for example, Japanese Patent Publication NO.Hei4-191465 or Japanese Patent Publication NO.Hei10-238446).
In such an ignition apparatus for internal combustion engine, a Zener diode is provided in parallel to the capacitor for preventing the capacitor from destruction, which is caused by an overcharge thereof. Moreover, in the ignition apparatus, a voltage at both ends or the capacitor is limited to be constant voltage. (100 to 300[V])
Thus, the ignition apparatus for internal combustion engine employing the capacitor as an electric power supply for generating the ionized current does not require to particularly provide an electric power supply (such as battery) exclusively used for supplying the ionized current. Therefore, parts of the ignition apparatus are reduced and miniaturization is realized.
However, in the ignition apparatus for internal combustion engine of the structure which discharges the capacitor charged with the secondary current flowing while generating a spark discharge at the spark plug, when turning on electricity in the primary winding for accumulating magnetic flux energy in the ignition coil, a high voltage (several kV) which has a opposed polarity to the high voltage for firing, is generated at the secondary winding, whereby the spark discharge of the spark plug is generated before a normal firing time. Therefore, this may bring about a misfire of the air-fuel mixture.
The above-mentioned ignition apparatus is structured such that a conductive path of the secondary current causes a current to be conductive in both directions, whereby the ignition apparatus makes it possible to charge the capacitor connected in series to the conductive path of the secondary current when generating the spark discharge at the spark plug and to discharge the capacitor when generating the ionized current between the electrodes of the spark plug. The ignition apparatus is structured such that the conductive path of the secondary current causes current to be conductive in both directions. Therefore, in such an ignition apparatus for internal combustion engine which is accompanied with changing of magnetic flux density in the ignition coil at starting conduction to the primary winding, an induced voltage having an opposed polarity thereof at the time to cut off the primary current, is generated at both ends of the secondary winding.
In case the induced voltage generated at the time to cut off the primary current is higher than a voltage value necessary to generate the spark discharge, the spark discharge is generated at the spark plug under a condition where the secondary current flows in a opposed direction to a secondary current flowing at the time of an inherent spark discharge.
Further, under a condition where the conduction of the primary current to the primary winding is constant, the rotation speed of the internal combustion engine is higher, a time of starting the conduction of the primary current to the primary winding is determined at xe2x80x9can earlier period of a crank anglexe2x80x9d. Herein, xe2x80x9cThe earlier period of the crank anglexe2x80x9d indicates xe2x80x9ca time when an internal pressure within a cylinder is lowxe2x80x9d.
It is known that the lower the internal pressure in the cylinder is, the lower the discharge voltage at he spark plug. Therefore, When the internal combustion engine operated at high rotation speed, a misfire of the air-fuel mixture is easy to happen, since the high voltage (several kV) of the opposed polarity to the high voltage for firing, which is generated in the secondary winding. at the time to start a conduction to the primary winding. In order to avoid generating the misfire of the air-fuel mixture at the earlier period (xe2x80x9ca time when an internal pressure within a cylinder is lowxe2x80x9d), it is necessary that a conductive direction in the conductive path of the secondary current is determined to be one direction and a so-called diode for preventing reverse current is provided between one end of the secondary winding and one end of the spark plug so that current is allowed to flow only when the time to cut off the primary current.
However, in case the diode for preventing reverse current is provided between one end of the secondary winding and one end of the spark plug so as to allow only the conduction of the secondary current in the secondary winding when the time to cut off the primary current, the ignition apparatus for internal combustion engine having the function generating the ionized current makes it possible to charge the capacitor by the secondary current, and the current by discharging from the capacitor cannot flow, whereby it is difficult to provide the ionized current between electrodes of the spark plug.
Therefore, the ionized current flowing between the electrodes of the spark plug cannot be detected.
It is an object of the invention to provide an ignition apparatus for internal combustion engine which can restrain a misfire of the air-fuel mixture caused by generating the spark discharge at the spark plug when the time to start a conduction to the primary winding, and can generate and detect the ionized current between electrodes of the spark plug.
According to the first aspect of the invention, an ignition apparatus for an internal combustion engine comprises:
an ignition coil comprising a primary winding and a secondary winding, wherein the secondary winding has a high voltage side and a low voltage side, and the ignition coil generates a firing voltage supplied to the secondary winding by cutting off a primary current flowing in the primary winding;
a switching device for conducting and cutting off the primary current;
a spark plug connected in series to the secondary winding to form a closing loop, wherein a spark discharge is generated in the spark plug when a secondary current generated by the firing voltage flows in the spark plug;
a diode for preventing a reverse current, connected to a conducting path between the spark plug and the high voltage side, wherein the diode conducts the secondary current when a primary current is cut off, the diode cuts off the secondary current when the primary current starts to flow;
a current detecting device connected in series to the secondary winding and the spark plug; and
a supplied voltage limiting device holding a voltage applied to the current, detecting device below a predetermined value, when the firing voltage is generated,
wherein an ionized current generating voltage is supplied to the secondary winding by a residual energy when the residual energy is remained in the ignition coil after the spark discharge, the current detecting device detects a current in proportion to the ionized current, which is generated when the ionized current generating voltage is supplied to the spark plug.
In short, in the ignition apparatus for internal combustion engine of the invention, the diode for preventing reverse current is provided in the conductive path connecting the high voltage side of the secondary winding of the ignition coil to the spark plug, thereby to limit the current conductive directions in the conductive path of the secondary current to be one direction.
The diode for preventing reverse current cuts off the conduction by a high voltage generated at both ends of the secondary winding when the time to start the conduction to the primary winding, so that the high voltage generated at both ends of the secondary winding when the time to start the conduction to the primary winding prevents a generation of the spark discharge between electrodes (a center electrode and an earth electrode) of the spark plug.
Further, in the ignition apparatus for internal combustion engine of the invention,
the spark plug is supplied with an induced voltage generated at both ends of the secondary winding by residual energy existing in the ignition coil after ending the spark discharge of the spark plug, thereby to conduct the ionized current between the electrodes of the spark plug.
To explain in more detail, the induced voltage generated at both ends of the secondary winding by the residual energy existing in the ignition coil after ending the spark discharge of the spark plug is supplied to the spark plug, and the induced voltage is charged in a floating capacitor existing in the conductive path of the secondary current. The floating capacitor existing in the conductive path of the secondary current includes a floating capacitor of the spark plug. This supplied electric charge to the floating capacitor is utilized to conduct the ionized current between the electrodes of the spark plug.
That is, the induced voltage supplied to both ends of the secondary winding by the residual energy of the ignition coil is used as a voltage for conducting the ionized current to generate the ionized current, and the ignition coil has a function as a power supply for generating the high voltage for firing to generate the spark discharge and as the power supply for generating the ionized current.
Herein, the residual energy existing in the ignition coil when ending the spark discharge of the spark plug, is insufficient for continuing the spark discharge, but has the sufficient amount for generating the ionized current by charging the floating capacitor in the conductive path of the secondary current. That is, the voltage for generating the ionized current at both ends of the secondary winding by the residual energy after ending the spark discharge is around 1 to 5 [kV].
Such a voltage for generating the ionized current at both ends of the secondary winding is higher than a voltage, which is 100 to 300 [V] in the related art, accumulated by a capacitor for generating an ionized current, which is supplied between electrodes of the spark plug. Therefore, a larger ionized current than the one in the related art flows between the electrodes of the spark plug, so that a detection accuracy of the ionized current can be improved.
Further, the induced voltage generated at both ends of the secondary winding after ending the spark discharge. accumulates electric charge in the floating capacitor existing in the conductive path of the secondary current, but the supplied electric charge accumulated in the floating capacitor of the spark plug is prevented from, back-flowing to the secondary winding by the diode for preventing reverse current provided in the conductive path, which connects the high voltage side of the secondary winding to the spark plug. Therefore, the supplied electric charge accumulated in the floating capacitor of the spark plug does not only flow back to the side of the secondary winding but also get consumed, so that the supplied electric charge is utilized for generating the ionized current between the electrodes of the spark plug. In short, the diode for preventing reverse current has a function of avoiding the misfire when the time to start the conduction of the primary winding and also a function of generating the ionized current between the electrodes of the spark plug.
A current detecting means is connected in series to the secondary winding and the spark plug existing in the conductive path of the secondary current. When the ionized current flows between the electrodes of the spark plug, a current flowing in the current detecting means is in proportion to the ionized current flowing between the electrodes, the ionized current can be preferably detected by detecting the current flowing in the current detecting means.
When the high voltage for firing (that is, the spark discharge) is generated, a supplied voltage limiting means limits an supplied voltage to the current detecting means below a predetermined value, thereby it is possible to limit a dropping rate of a supplied voltage to the current detecting means below the predetermined value. The dropping rate of the supplied voltage to the current detecting means is included in the high voltage for firing is generated in the secondary winding. Therefore, the supplied voltage to the spark plug can be prevented from decreasing. It is possible to prevent the misfire without generating the spark discharge and a termination of the spark discharge in a short time period.
According to the first aspect of the invention, a misfire of the air-fuel mixture when the time to start the conduction to the primary winding is prevented, and the internal combustion engine in the present invention maybe avoided from injuries by the misfire of the air-fuel mixture.
In addition, by making use of the induced voltage (the voltage for generating the ionized current) generated by the residual energy existing in the ignition coil after ending the spark discharge of the spark plug, and by serving the diode for preventing reverse current provided in the conductive path connecting the high voltage side of the secondary winding and the spark plug, the ionized current can be generated between the electrodes of the spark plug.
When supplying a voltage between the electrodes of the spark plug for generating the ionized current, in comparison with the case of supplying a voltage such that the center electrode of the spark plug is negative and the earth electrode thereof is positive, in the case of supplying a voltage such that the center electrode of the spark plug is positive and the earth electrode thereof is negative, it is known that a larger ionized current can be generated. This is why an ion is provided with an electron from the earth electrode having a larger surface compared with a surface area of the center electrode, whereby more electrons are exchanged and movable.
From this fact, in the ignition apparatus for internal combustion engine of the invention, it is sufficient that the ignition coil and the spark plug are provided such that the voltage for generating the ionized current generated at both ends of the secondary winding by the residual energy in the ignition coil after ending the spark discharge of the spark plug is supplied in such a manner that the center electrode of the spark plug is positive. The detecting precision of the ionized current can be more heightened thereby.
For accomplishing this effect, when cutting off the conduction of the primary current, the ignition coil (actually, the winding direction of the secondary winding) to be connected to the spark plug is adjusted such that the center electrode of the ignition coil is positive.
As to the current detecting means for detecting a current in proportion to the ionized current, for example, as seen in a second aspect of the invention, the current detecting means is a detecting resistor one end of which is connected to the low voltage side of the secondary winding, while the other end thereof is grounded. The current detecting means detects the voltage between both ends of the detecting resistor, which is in proportion to the ionized current.
Thus, in the detecting resistor one end of which is connected to the low voltage side of the secondary winding, and the other end is connected to the detecting resistor earthed, the voltage in proportion to the ionized current flowing between the electrodes of the spark plug is generated between both ends of the detecting resistor, when supplied the voltage for generating the ionized current to the spark plug in order to conduct the ionized current between the electrodes of the spark plug.
Therefore, by measuring change of the voltage between both ends of the detecting resistor and calculating the current flowing in the detecting resistor on the basis of the measured voltage at both ends and the resistance value of the detecting resistor, the magnification of the ionized current can be detected.
Further, the detecting resistor is grounded at one end thereof, and a potential of the earthed end is maintained predetermined (ground potential (0[V])), and by detecting change of the potential at the end connected to the low voltage side of the secondary winding as a standard potential being the ground potential, the voltage at both ends of the detecting resistor can be preferably detected.
Thus, according to the second aspect of the invention, the magnitude of the ionized current flowing between the electrodes of the spark plug can be detected, and the misfiring of the internal combustion engine and the knocking can be judged by the ionized current detected on the basis of this detecting resistor.
Further, the ignition apparatus for internal combustion engine of the second aspect of the invention is, as set forth in the third aspect of the invention, the supplied voltage limiting means may be structured to include a Zener diode connected in parallel to the detecting resistor in such a mode that an anode is connected between an one end of connecting the low pressure side of the secondary winding and one end of the detecting resistor.
That is, when the voltage at both ends of the detecting resistor is above the breakdown voltage of the Zener diode, the Zener diode makes the current conductive, thereby to limit the supplied voltage to the detecting resister below a predetermined value for limiting the voltage at both ends of the detecting resistor to exceedingly rise. Therefore, the discharge current (the secondary current) flowing when the time to generate the spark discharge does not flow to the detecting resistor but is bypassed by the Zener diode, whereby a property of a spark discharge of the spark plug and a firing of the air-fuel mixture can be maintained well conditioned.
It is sufficient that the breakdown voltage of the Zener diode (the Zener voltage) is set at around dynamic range (for example, around 5[V] or 8[V]) of the ionized current to be detected by the detecting resistor, namely, in response to maximum voltage values at both ends of the detecting resistor, which is generated by the ionized current flowing between the electrodes of the spark plug.
It is thereby possible to preferably realize detection of the ionized current using the detecting resistor. As the Zener diode, cheap ones maybe used where withstand electric power is around 0.1[W] to 1[W].
Thus, depending on the ignition apparatus for internal combustion engine of the invention (the third aspect of the invention), not only the detecting resistor may be protected, but also the misfiring or expiration of the spark discharge in a short time may be avoided, so that the firing facility to the air-fuel mixture can be prevented from reducing and the operating facility of the internal combustion engine can be prevented from lowering.